The notion of a social network has turned out to be useful for explaining many real-world phenomena. A social network is a social structure usually made of individuals, groups of individuals, or organizations corresponding to “nodes,” which are tied (connected) by one or more specific types of interdependency, such as friendship, kinship, knowledge, and the like. “Online” friends and acquaintances may have significant influence on people; perhaps as much as friends who are interacted with using traditional modes of interaction, such as face-to-face interactions that do not involve computing technologies.